Nietzsche says “a casual stroll through the lunatic asylum shows that faith does not prove anything”.

Faith is at rest unless we gain new experience that is different from previous one. For example, if we left our home town many years ago, when we come back, we will be surprised by its change. The impression of your home town in your mind is at rest and not changed. Similarly, lots of faiths in our mind are at rest but in fact it has changed a long time ago. Therefore, we lived in illusion most of the time.